PROJECT SUMMARY Participation in a variety of youth sports and physically active programs has served as an important avenue for childhood growth and development, both physically and psychosocially. However, this traditional paradigm is currently being challenged as early sports specialization (ESS) becomes progressively more common in adolescence and even childhood. ESS is defined as intense training in a single sport to the exclusion of other types of physical activity. Clinicians and researchers are increasingly concerned about the potential effects of this model, which inherently places focus on elite athlete development as opposed to youth health and development. This change in focus combined with our limited understanding of ESS effects, results in mixed messaging among parents, coaches, clinicians and other leaders regarding benefits and drawbacks of ESS. Although evidence-based research is increasingly available regarding potential harms and benefits of ESS, serious and substantial knowledge gaps currently preclude a full understanding of ESS effects on motor control development, musculoskeletal injury risk, health-related quality of life, and optimal strategies for appropriate youth training and development. There is a known steep decline in sports participation and physical activity among adolescents (especially girls). This, coupled with known public health concerns of inactivity among youth, obviate the need to identify and address these gaps and develop evidence-based recommendations to optimize the health, safety, development of youth via sport. Thus, the purpose of this daylong conference is to conduct a rigorous review of current scientific knowledge, identify important knowledge gaps, and most notably create a set of research priorities related to youth sports specialization and athlete health and development. The conference will be held as a pre-conference to the American Medical Society for Sports Medicine's annual meeting in Houston, Texas and will involve clinicians, researchers, and advocacy group representatives from the myriad stakeholders affected by ESS. The conference focuses on evidence-based results and recommendations; however, it will also allow for thoughtful interaction and solution-oriented discussion from multiple participants representing diverse backgrounds via numerous panel sessions and break-out groups. At the conclusion of the conference, select representatives will synthesize the systematic reviews and discussions by developing a research agenda to guide and prioritize future investigation and innovation in this area. The research conference aims to attract over 150 multi-disciplinary individuals, and results will be disseminated through academic journals, websites, social media postings, and annual meetings of each organization and representative?as well as through marketing channels of key advocacy groups. This conference will highlight what is known and unknown, and identify vital next research questions allowing researchers, clinicians, parents, coaches and athletes to progress in the quest to optimize healthy youth development through sport.